Cleaning brass.

I’ll pop down Barnsley docks.

 

It’s just muck….ingrained muck.

 

Is that called de-zincification, where some of the zinc content is dissolved away?

 

Yep

 

Have a word with @snotty as he's our resident "Down the docks" expert!
Usually on a Friday night from what I hear!

 

We used to call is fooked! But in essence harsh chemicals like vinegar and coke tended to do what you describe @Meltman .

Having checked with some diving friends, they now just use abrasive and then Brasso.

 

Where there's muck there's brass, lad.

 

He did mention something about a shiny ring!

 

I’ve used Duraglit on a few brass and copper things. Worked well.